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_11 for which if x_11 were a lawyer, then x_11 is taking a plane. For all x_11, x_11 is a lawyer if and only if x_11 is sad. For all x_11, if x_11 takes a plane, then x_11 is sad.
There is at least one x_11 for which if x_11 were a lawyer, then x_11 is sad can be inferred via the existential transitivity rule. For all x_11, if x_11 were a lawyer, then x_11 is sad can be inferred via the universal biconditional elimination rule. For all x_11, if x_11 were sad, then x_11 is a lawyer can be inferred via the universal biconditional elimination rule.