What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: There is at least one x_7 for which if x_7 were sad, then x_7 is a sailor. For all x_7, if x_7 plays squash, then x_7 is sad. For all x_7, if x_7 were a sailor, then x_7 is sad.
There is at least one x_7 for which if x_7 plays squash, then x_7 is a sailor can be inferred via the existential transitivity rule. There is at least one x_7 for which x_7 is sad if and only if x_7 is a sailor can be inferred via the existential biconditional introduction rule. There is at least one x_7 for which x_7 is a sailor if and only if x_7 is sad can be inferred via the existential biconditional introduction rule.