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: For all x_6, if x_6 were an astronaut, then x_6 is not climbing a mountain. For all x_6, x_6 is an astronaut or x_6 will play squash. There is at least one x_6 for which x_6 will write a letter. For all x_6, x_6 will climb a mountain.
For all x_6, x_6 is not an astronaut can be inferred via the universal modus tollens rule. There is at least one x_6 for which x_6 will write a letter and x_6 will climb a mountain can be inferred via the existential conjunction rule. There is at least one x_6 for which x_6 will climb a mountain and x_6 will write a letter can be inferred via the existential conjunction rule.