{HEAD ~ Y} is {TAIL ~ hydrogen} or the organic residue of a saturated or unsaturated organic compound containing at least one isocyanate reactive active hydrogen atom, which residue remains after reaction of at least one such active hydrogen atom with an isocyanate moiety 
is
{ HEAD ~ Y } is { TAIL ~ hydrogen } or the organic residue of a saturated or unsaturated organic compound containing at least one isocyanate reactive active hydrogen atom , which residue remains after reaction of at least one such active hydrogen atom with an isocyanate moiety
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH