A functor $F : A \to B$ is said to be opaque if for each $a,a\tick\in A_o$ and $b : Fa\to Fa\tick$ in $ B$ there is a zig-zag in $A$, the image of which under $F$ fits into a lantern diagram
A functor $F : A \to B$ is said to be opaque if for each $a,a\tick\in A_o$ and $b : Fa\to Fa\tick$ in $ B$ there is a zig-zag in $A$, the image of which under $F$ fits into a lantern diagram