Full Idea
When looking for a proof of a sequent, the best we can do in natural deduction is to work simultaneously in both directions, forward from the premisses, and back from the conclusion, and hope they will meet in the middle.
Gist of Idea
In natural deduction we work from the premisses and the conclusion, hoping to meet in the middle
Source
David Bostock (Intermediate Logic [1997], 6.5)
Book Reference
Bostock,David: 'Intermediate Logic' [OUP 1997], p.270
Related Idea
Idea 13757 Unlike natural deduction, semantic tableaux have recipes for proving things [Bostock]