I read the following in the Nomicon:
Coercion is allowed between the following types:
Transitivity:
T_1
toT_3
whereT_1
coerces toT_2
andT_2
coerces toT_3
.
I could not find an example which proves it. I can not think of two types that have no implicit coercion between them but there is a third type that has an implicit coercion between those two.
This is the first time I came across this great concept so I'd be glad to see a real example.