Editing Register machine (section)

=== Melzak's (1961) model is different: clumps of pebbles go into and out of holes ===
Melzak's (1961)<ref name="Melzak_1961"/> model is significantly different. He took his own model, flipped the tapes vertically, called them "holes in the ground" to be filled with "pebble counters". Unlike Minsky's "increment" and "decrement", Melzak allowed for proper subtraction of any count of pebbles and "adds" of any count of pebbles.

He defines indirect addressing for his model<ref name="Melzak_1961"/>{{rp|page=288}} and provides two examples of its use;<ref name="Melzak_1961"/>{{rp|page=89}} his "proof"<ref name="Melzak_1961"/>{{rp|pages=290–292}} that his model is Turing equivalent is so sketchy that the reader cannot tell whether or not he intended the indirect addressing to be a requirement for the proof.

Legacy of Melzak's model is Lambek's simplification and the reappearance of his mnemonic conventions in Cook and Reckhow 1973.<ref name="Cook-Reckhow_1973"/>