The ``path cut'' operator

In addition to the DATR nodes described below, we propose the addition of a (built-in) ``path cut'' operator (notated by a period) to discard path extensions.

    Path_cut_demo:
        <cut>   == Idem:<a b c .>
        <uncut> == Idem:<a b c>.
    
    Path_cut_demo:<cut d e f>   = a b c.
    Path_cut_demo:<uncut d e f> = a b c d e f.