Add returns as value a sequence of integers created by adding the First element of the path to each element in the (interger prefix of the) Rest. Add fails if the path prefix contains less than two integers.
Add:<100 2 3 4> = 102 103 104.
Add:<100 2 3 4 foo 2 3 4> = 102 103 104 foo 2 3 4.
Add:<-1 102 103 104> = 101 102 103.
Add:<-1 102 103 104 foo> = 101 102 103 foo.
