Question
Prove that the following arguments are standard by constructing metaphorical proof
$(P\ v\ R)\ \rightarrow (S\ v\ T)$
$\sim M\ \&\ \sim N$
$N\ v \sim (S\ v\ T)$
$H \rightarrow (P\ v\ R)$
$[\sim H\ \&\ \sim (P\ v\ R)]\ v\ S$

Answer

$(1)\ (P v R)\ \rightarrow (S\ v\ T)$ $P$
$(2)\ \sim M\ \&\ \sim N$ $P$
$(3)\ N\ v\ \sim (S\ v\ T)$ $P$
$(4)\ H \rightarrow (P\ v\ R)$ $P/ [\sim H\ \&\ \sim (P\ v\ R) ]\ v \ S$
$(5)\ \sim N$ $2,$ Simp.
$(6)\ \sim (S\ v\ T)$ $3, 5, DS$
$(7)\ \sim (P\ v\ R)$ $1, 6, MT$
$(8)\ \sim H$ $4, 7, MT$
$(9)\ \sim H\ \&\ \sim (P\ v\ R)$ $8, 7,$ Conj.
$(10)\ [\sim H\ \&\ \sim (P\ v\ R)\ ]\ v\ S$ $9,$ Add

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