The concept of developmental constraint

In Chapter 7 the concept of developmental constraint for species x is defined as the boundary between the two sets DPFx = {f| f = developmentally possible forms for species x} and DIFx = {f| f = developmentally impossible forms for species x} (Fig. 7.5). Forms that belong to the set DPFx, developmentally possible form for species x, must be phylogenetically possible and geometrically possible, belonging to the sets PPFx and GPF, but can either be functional (DPFx ∩ FPF) or lethal (DPFx ∩ NPF). Actual existent form for species x can only belong to the former set intersection, such that potential existent form for species x, PEFx, is constrained to be PEFx ⊂ DPFx ⊂ FPF ⊂ GPF = {f| f ∈ GPF, f ∈ FPF, f ∈ DPFx} (Fig. 7.6).