Whethere the automaton is letterized, i.e. each transition is labeled by a single letter. It's always true when labels are letters, for example.
a1 = vcsn.b.expression("ab+c*").standard() a1
Here, no computation is done, the result is implied by the labelset.
ctx = vcsn.context("law_char, b") a2 = ctx.expression("a+bc*").standard() a2
Here, as labels can be words, each transition's label is checked to see that it is a letter (or the empty word).
a3 = ctx.expression("abc").standard() a3