Help with Narsese

[kripper]

What am I doing wrong here?

// ariel is father of chris
( ariel * chris ) --> father_of >.

// chris is father of angel
< ( chris * angel ) --> father_of >.

// Definition of grandpa
<($1 * $3) --> grandpa_of> <=> (&&, <($1 * $2) --> father_of>, <($2 * $3) --> father_of>)>.

100

// who is grandpa of angel?
< ( ?1 * angel ) --> grandpa_of >?

// Answer: None.
// Expected anwer: ariel