Commuting pairs of elements in monoids
We define the predicate
commute a b := a * b = b * a and provide some operations on terms
commute a b). E.g., if
b, and c are elements of a semiring, and that
hb : commute a b and
hc : commute a c. Then
hb.pow_left 5 proves
commute (a ^ 5) b and
(hb.mul_right hc) proves
commute a (b ^ 2 + b * c).
Lean does not immediately recognise these terms as equations, so for rewriting we need syntax like
rw [(hb.pow_left 5).eq] rather than just
rw [hb.pow_left 5].
This file defines only a few operations (
inv_right, etc). Other operations
pow_right, field inverse etc) are in the files that define corresponding notions.
Most of the proofs come from the properties of