Replacement rules tests

`ReplaceAll` (`/.`)

Replaces parts of an expression according to rules.

$ wo '{a, b} /. a -> x'
{x, b}

`ReplaceRepeated` (`//.`)

Repeatedly applies transformation rules until no more changes occur.

$ wo 'ReplaceRepeated[f[2] -> 2][f[f[f[f[2]]]]]'
2

$ wo 'f[f[f[f[2]]]] //. f[2] -> 2'
2