65-73, 1980. The original paper had no abstract, so this reprint to be truthful to the original work is published with no abstract. Mathematical subject classification: 35J25, 35Q60, 47F05, 86A20, ...

The Dubai student scored an impressive 'A*' in his GCSE mathematics exam. A year later, he secured a topper-worthy A** in a further mathematics paper, and come August, he's expecting good news ...