Do the skill focus and the 13+ ranks have to be in the same skill? If not then it is very easy.
In a Pre-req
~ We need 13+ ranks in any skill
foreach pick in hero from BaseSkill
validif (each.field[kUserRanks].value >= 13)
nexteach
In an Expr-req
~ We need skill focus and it doesn't matter which
#hasfeat[fSkillFoc] <> 0
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