In the early 1930s MacColl [1] noticed that quantum tunneling appears to take no time or little time, in the sense that the peak of a wave packet, transmitted across a classically forbidden region, may arrive at a detector earlier than that of the freely propagating one. If the advanced peak is used to predict the time τ the particle has spent in the barrier region, the result is nearly zero. D...

In 2010, Spence and Van Gelder presented a family of CNF formulas based on combinatorial block designs. They showed empirically that this construction yielded small instances that were orders of magnitude harder for state-of-the-art SAT solvers than other benchmarks of comparable size, but left open the problem of proving theoretical lower bounds. We establish that these formulas are exponentia...