Table 2.

Two evaluation algebras for the Sankoff problem

SIGNATURE		PROB	SIM
nil	$=$	0	0
NoStr (x, y)	$=$	x + y	x + y
Split (x, y)	$=$	x + y	x + y
Pair $(⟨a,b⟩,x,⟨c,d⟩)$	$=$	x + $\mathrm{\Psi }(a,c)$ + $\mathrm{\Psi }(b,d)$	x + $\mathit{\sigma }(a,b)$ + $\mathit{\sigma }(c,d)$	(*)
Ins $(⟨\mathit{ϵ},b⟩)$	$=$	0	$\mathit{\gamma }(b)$
Del $(⟨a,\mathit{ϵ}⟩)$	$=$	0	$\mathit{\gamma }(a)$
Match $(⟨a,b⟩)$	$=$	0	$\mathit{\sigma }(a,b)$
$\mathit{\phi }$	$=$	Max	Mx