Is it permissible to marry a woman if it becomes apparent that her paternal half-sister nursed the suitor once?

It is permissible to marry the betrothed woman, so long as her paternal sister was suckled by her only once, because the suckling that prohibits marriage is five sucklings. The limit of a suckling is counted by the infant latching onto the breast and suckling from it, then leaving it by his own will.