ADVICE on choosing a rule appropriate to the operator '(∃x)' (ONE OR MORE x)
| suggestions: | ||
| If (∃x) | is the Main Operator in a PREMISE, | EI CQ |
| the MO in the GOAL or CONCLUSION, | EG CQ | |
| to be LEFT AS IS while others change, | any equivalence that fits the other operators. | |
| to be REPLACED with another operator, | CQ DN TAUT |
Note: if the conclusion or goal proposition is IDENTICAL to a portion of a premise, then chose the rule according to that PREMISE'S main operator.
If you wish to apply an inference to the quantified expression then you must apply EI first, but equivalence rules may be applied without first using EI.