operator: exp-max

    description:
        exp-max[op] |x>
        exp(op) applied to |x>, ignoring factors of 1/n!
        if you want the 1/n! too, then see full-exp
        cf: exp(A) |Psi> in quantum mechanics
        ie: (1 + op + op^2 + ... + op^n) |x>
        where we go to full depth
        ie, n is such that len(exp[op, n] |x>) == len(exp[op, n+1] |x>)

    examples:
        -- load a binary tree:
        load tree.sw

        -- entire left branch of tree:
        exp-max[left] |x>
            n: 4
            |x> + |0> + |00> + |000> + |0000>
            
        -- full tree starting from |11>:
        exp-max[child] |11>
            n: 2
            |11> + |110> + |111> + |1100> + |1101> + |1110> + |1111>
        
        -- find the lengths of the node names in the full tree:
        ket-length exp-max[child] |x>
            n: 4
            3|number: 1> + 4|number: 2> + 8|number: 3> + 16|number: 4>

    see also:
        exp, full-exp