Replace

Replace(expr, lhs -> rhs)

replaces the left-hand-side pattern expression lhs in expr with the right-hand-side rhs.

Replace(expr, {lhs1 -> rhs1, lhs2 -> rhs2, ... } )

replaces the left-hand-side patterns expression lhsX in expr with the right-hand-side rhsX.

Examples

>> Replace(x, {{e->q, x -> a}, {x -> b}})
{a,b}