[r-t] Grandsire Triples

[Stephen Penney]

AH: "It has been a bit quiet recently.  Come on, someone give us an amusing
problem to work on...."

In the absence of an interesting problem:
I was told once that Grandsire Triples can be called round from any change
using three calls or less.
I've failed to find a proof for this, in terms of logical reasoning.

It is true though - Geoff Dodds gave me a list of all the possible leadheads
with the necessary calls to bring them round.

Percy