A strict symmetric premonoidal category is a category P together with:
such that:
This definition is based on Power's presentation of Power and Robinson's definition.
A three-coloured flow graph over three signatures V, C and P with the same sorts is a two-coloured flow graph over V and C except that:
Identity: | Composition: |
Tensor left: | |
Tensor right: | |
Symmetry: |
We can now replay the same proof of soundness and completeness as in the finite products case. In each case, the proof of the theorems is so similar to that in the finite products case that we elide it.
Let Graph(V,C,P) be the category of acyclic flow graphs over (V,C,P) where the morphisms from X to Y are graphs from XS to YS, viewed up to bisimulation.
Proposition (Bisimulation is a congruence). Bisimulation is a congruence wrt the graph operations.
Proposition (Flow graphs form a premonoidal category). Graph(V,C,P) is a premonoidal category over P with centre Graph(V,C).
Define Term(V,C,P) as the free premonoidal category over P with central category Term(V,C).
f,g | ::= | f | |
| | f ; g | ||
| | f g | ||
| | f g | ||
| | c |
If terms can be proved equal using the axioms for a premonoidal category we shall write f = g.
Proposition (Soundness). If f = g then [[f]] [[g]].
Proposition (Expressivity). For any graph G, there is a term f such that [[f]] G.
A term is in normal form (ranged over by n) iff it is of the form:
n | ::= | |
| | ||
| | ||
| | ||
| |
Proposition (Cancellation of permutations). For any:
Proposition (Cancellation of val nodes). For any:
Proposition (Cancellation of central nodes). For any:
Proposition (Cancellation of proc nodes). For any:
Proposition (Completeness). If [[f]] [[g]] then f = g.
Proposition (Initiality). Graph(V,C,P) is the initial strict symmetric premonoidal category over P with Graph(V,C) as centre.