pep8 --ignore=W291,W293,E302
extract pair_node_to_var into function so that it can be reused
improve docstring and fix typo
add check of variable types in AST wrt given domain definitions
use double quotes in example

that this escaped to become input to jtlv that could synthesize a machine that doesn't satisfy the initial condition (caught in synth.strategy2mealy) motivated introducing variable type checks in e8072ad45557dd2776e54c1d33a4a8832038053c.