72 lines
2 KiB
Text
72 lines
2 KiB
Text
/-
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Copyright (c) 2014 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Module: data.num
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Author: Leonardo de Moura
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-/
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import logic.eq
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open bool
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namespace pos_num
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theorem succ_not_is_one (a : pos_num) : is_one (succ a) = ff :=
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induction_on a rfl (take n iH, rfl) (take n iH, rfl)
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theorem pred.succ (a : pos_num) : pred (succ a) = a :=
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rec_on a
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rfl
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(take (n : pos_num) (iH : pred (succ n) = n),
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calc
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pred (succ (bit1 n)) = cond (is_one (succ n)) one (bit1 (pred (succ n))) : rfl
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... = cond ff one (bit1 (pred (succ n))) : succ_not_is_one
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... = bit1 (pred (succ n)) : rfl
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... = bit1 n : iH)
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(take (n : pos_num) (iH : pred (succ n) = n), rfl)
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section
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variables (a b : pos_num)
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theorem add.one_one : one + one = bit0 one :=
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rfl
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theorem add.one_bit0 : one + (bit0 a) = bit1 a :=
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rfl
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theorem add.one_bit1 : one + (bit1 a) = succ (bit1 a) :=
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rfl
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theorem add.bit0_one : (bit0 a) + one = bit1 a :=
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rfl
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theorem add.bit1_one : (bit1 a) + one = succ (bit1 a) :=
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rfl
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theorem add.bit0_bit0 : (bit0 a) + (bit0 b) = bit0 (a + b) :=
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rfl
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theorem add.bit0_bit1 : (bit0 a) + (bit1 b) = bit1 (a + b) :=
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rfl
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theorem add.bit1_bit0 : (bit1 a) + (bit0 b) = bit1 (a + b) :=
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rfl
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theorem add.bit1_bit1 : (bit1 a) + (bit1 b) = succ (bit1 (a + b)) :=
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rfl
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end
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theorem mul.one_left (a : pos_num) : one * a = a :=
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rfl
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theorem mul.one_right (a : pos_num) : a * one = a :=
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induction_on a
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rfl
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(take (n : pos_num) (iH : n * one = n),
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calc bit1 n * one = bit0 (n * one) + one : rfl
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... = bit0 n + one : iH
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... = bit1 n : add.bit0_one)
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(take (n : pos_num) (iH : n * one = n),
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calc bit0 n * one = bit0 (n * one) : rfl
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... = bit0 n : iH)
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end pos_num
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