insert

$maria isa person, has name "Maria";
$paolo isa person, has name "Paolo";
$andrea isa person, has name "Andrea";
$sue isa person, has name "Sue";

$f1 (caller:$maria, callee:$andrea) isa call;
$f2 (caller:$maria, callee:$paolo) isa call;
$f3 (caller:$paolo, callee:$sue, callee:$andrea) isa call;