(* Title: HOL/ex/Arith_Examples.thy

Author: Tjark Weber

*)

header {* Arithmetic *}

theory Arith_Examples

imports Main

begin

text {*

The @{text arith} method is used frequently throughout the Isabelle

distribution. This file merely contains some additional tests and special

corner cases. Some rather technical remarks:

@{ML Lin_Arith.simple_tac} is a very basic version of the tactic. It performs no

meta-to-object-logic conversion, and only some splitting of operators.

@{ML Lin_Arith.tac} performs meta-to-object-logic conversion, full

splitting of operators, and NNF normalization of the goal. The @{text arith}

method combines them both, and tries other methods (e.g.~@{text presburger})

as well. This is the one that you should use in your proofs!

An @{text arith}-based simproc is available as well (see @{ML

Lin_Arith.simproc}), which---for performance

reasons---however does even less splitting than @{ML Lin_Arith.simple_tac}

at the moment (namely inequalities only). (On the other hand, it

does take apart conjunctions, which @{ML Lin_Arith.simple_tac} currently

does not do.)

*}

subsection {* Splitting of Operators: @{term max}, @{term min}, @{term abs},

@{term minus}, @{term nat}, @{term Divides.mod},

@{term Divides.div} *}

lemma "(i::nat) <= max i j"

by linarith

lemma "(i::int) <= max i j"

by linarith

lemma "min i j <= (i::nat)"

by linarith

lemma "min i j <= (i::int)"

by linarith

lemma "min (i::nat) j <= max i j"

by linarith

lemma "min (i::int) j <= max i j"

by linarith

lemma "min (i::nat) j + max i j = i + j"

by linarith

lemma "min (i::int) j + max i j = i + j"

by linarith

lemma "(i::nat) < j ==> min i j < max i j"

by linarith

lemma "(i::int) < j ==> min i j < max i j"

by linarith

lemma "(0::int) <= abs i"

by linarith

lemma "(i::int) <= abs i"

by linarith

lemma "abs (abs (i::int)) = abs i"

by linarith

text {* Also testing subgoals with bound variables. *}

lemma "!!x. (x::nat) <= y ==> x - y = 0"

by linarith

lemma "!!x. (x::nat) - y = 0 ==> x <= y"

by linarith

lemma "!!x. ((x::nat) <= y) = (x - y = 0)"

by linarith

lemma "[| (x::nat) < y; d < 1 |] ==> x - y = d"

by linarith

lemma "[| (x::nat) < y; d < 1 |] ==> x - y - x = d - x"

by linarith

lemma "(x::int) < y ==> x - y < 0"

by linarith

lemma "nat (i + j) <= nat i + nat j"

by linarith

lemma "i < j ==> nat (i - j) = 0"

by linarith

lemma "(i::nat) mod 0 = i"

(* rule split_mod is only declared by default for numerals *)

using split_mod [of _ _ "0", arith_split]

by linarith

lemma "(i::nat) mod 1 = 0"

(* rule split_mod is only declared by default for numerals *)

using split_mod [of _ _ "1", arith_split]

by linarith

lemma "(i::nat) mod 42 <= 41"

by linarith

lemma "(i::int) mod 0 = i"

(* rule split_zmod is only declared by default for numerals *)

using split_zmod [of _ _ "0", arith_split]

by linarith

lemma "(i::int) mod 1 = 0"

(* rule split_zmod is only declared by default for numerals *)

using split_zmod [of _ _ "1", arith_split]

by linarith

lemma "(i::int) mod 42 <= 41"

by linarith

lemma "-(i::int) * 1 = 0 ==> i = 0"

by linarith

lemma "[| (0::int) < abs i; abs i * 1 < abs i * j |] ==> 1 < abs i * j"

by linarith

subsection {* Meta-Logic *}

lemma "x < Suc y == x <= y"

by linarith

lemma "((x::nat) == z ==> x ~= y) ==> x ~= y | z ~= y"

by linarith

subsection {* Various Other Examples *}

lemma "(x < Suc y) = (x <= y)"

by linarith

lemma "[| (x::nat) < y; y < z |] ==> x < z"

by linarith

lemma "(x::nat) < y & y < z ==> x < z"

by linarith

text {* This example involves no arithmetic at all, but is solved by

preprocessing (i.e. NNF normalization) alone. *}

lemma "(P::bool) = Q ==> Q = P"

by linarith

lemma "[| P = (x = 0); (~P) = (y = 0) |] ==> min (x::nat) y = 0"

by linarith

lemma "[| P = (x = 0); (~P) = (y = 0) |] ==> max (x::nat) y = x + y"

by linarith

lemma "[| (x::nat) ~= y; a + 2 = b; a < y; y < b; a < x; x < b |] ==> False"

by linarith

lemma "[| (x::nat) > y; y > z; z > x |] ==> False"

by linarith

lemma "(x::nat) - 5 > y ==> y < x"

by linarith

lemma "(x::nat) ~= 0 ==> 0 < x"

by linarith

lemma "[| (x::nat) ~= y; x <= y |] ==> x < y"

by linarith

lemma "[| (x::nat) < y; P (x - y) |] ==> P 0"

by linarith

lemma "(x - y) - (x::nat) = (x - x) - y"

by linarith

lemma "[| (a::nat) < b; c < d |] ==> (a - b) = (c - d)"

by linarith

lemma "((a::nat) - (b - (c - (d - e)))) = (a - (b - (c - (d - e))))"

by linarith

lemma "(n < m & m < n') | (n < m & m = n') | (n < n' & n' < m) |

(n = n' & n' < m) | (n = m & m < n') |

(n' < m & m < n) | (n' < m & m = n) |

(n' < n & n < m) | (n' = n & n < m) | (n' = m & m < n) |

(m < n & n < n') | (m < n & n' = n) | (m < n' & n' < n) |

(m = n & n < n') | (m = n' & n' < n) |

(n' = m & m = (n::nat))"

(* FIXME: this should work in principle, but is extremely slow because *)

(* preprocessing negates the goal and tries to compute its negation *)

(* normal form, which creates lots of separate cases for this *)

(* disjunction of conjunctions *)

(* by (tactic {* Lin_Arith.tac 1 *}) *)

oops

lemma "2 * (x::nat) ~= 1"

(* FIXME: this is beyond the scope of the decision procedure at the moment, *)

(* because its negation is satisfiable in the rationals? *)

(* by (tactic {* Lin_Arith.simple_tac 1 *}) *)

oops

text {* Constants. *}

lemma "(0::nat) < 1"

by linarith

lemma "(0::int) < 1"

by linarith

lemma "(47::nat) + 11 < 8 * 15"

by linarith

lemma "(47::int) + 11 < 8 * 15"

by linarith

text {* Splitting of inequalities of different type. *}

lemma "[| (a::nat) ~= b; (i::int) ~= j; a < 2; b < 2 |] ==>

a + b <= nat (max (abs i) (abs j))"

by linarith

text {* Again, but different order. *}

lemma "[| (i::int) ~= j; (a::nat) ~= b; a < 2; b < 2 |] ==>

a + b <= nat (max (abs i) (abs j))"

by linarith

end