set X = { C where C is firing-sequence of N : ex q1, q2 being FinSubsequence st
( C = q1 \/ q2 & q1 misses q2 & Seq q1 in R1 & Seq q2 in R2 )
}
;
{ C where C is firing-sequence of N : ex q1, q2 being FinSubsequence st
( C = q1 \/ q2 & q1 misses q2 & Seq q1 in R1 & Seq q2 in R2 ) } c= N *
proof
let x be object ; :: according to TARSKI:def 3 :: thesis: ( not x in { C where C is firing-sequence of N : ex q1, q2 being FinSubsequence st
( C = q1 \/ q2 & q1 misses q2 & Seq q1 in R1 & Seq q2 in R2 )
}
or x in N * )

assume x in { C where C is firing-sequence of N : ex q1, q2 being FinSubsequence st
( C = q1 \/ q2 & q1 misses q2 & Seq q1 in R1 & Seq q2 in R2 )
}
; :: thesis: x in N *
then ex C being firing-sequence of N st
( x = C & ex q1, q2 being FinSubsequence st
( C = q1 \/ q2 & q1 misses q2 & Seq q1 in R1 & Seq q2 in R2 ) ) ;
hence x in N * ; :: thesis: verum
end;
hence { C where C is firing-sequence of N : ex q1, q2 being FinSubsequence st
( C = q1 \/ q2 & q1 misses q2 & Seq q1 in R1 & Seq q2 in R2 ) } is process of N ; :: thesis: verum