> as lemmas

1957 Z. S. Harris in Language 33 302 There exist morphemes whose X-co-occurrents (for each class X in constructional relation to them), in each sentence, equal the X-co-occurrents of a morpheme (of class Y) occupying a stated position (or one of several stated positions), relative to them, in the same sentence (or sequence of sentences), and whose total X-co-occurrents in all the appearances of these morphemes equal the sum of X-co-occurrents of all members of the class Y (which occupies the stated position relative to them). Such morphemes will be called pro-morphemes of the class Y, or pro-Y.

1965 Language 41 246 NkS = N: NkS ← S where S contains N as a constituent and in the derived kS an appropriate k-pro-morpheme is substituted for N of the source sentence.