Template:cpp/experimental/ranges/equality preservation

Equality preservation
An expression is equality preserving if it results in equal outputs given equal inputs.
 * The inputs to an expression consist of its operands.
 * The outputs of an expression consist of its result and all operands modified by the expression (if any).

Every expression required to be equality preserving is further required to be stable: two evaluations of such an expression with the same input objects must have equal outputs absent any explicit intervening modification of those input objects.