The chalk marks are transient, the formulas eternal.

Related:

• I will not squeak
  chalk...
• Complete
  Transient...
• transient bus
  protocol...
• I WILL NOT WASTE CHALK I WILL NOT WASTE CHALK I WILL
  NOT WASTE CHALK I WILL NOT WASTE CHALK Bart Simpson...
• I WILL NOT SQUEAK CHALK I WILL NOT SQUEAK CHALK I WILL
  NOT SQUEAK CHALK I WILL NOT SQUEAK CHALK Bart Simpson...
• Nobody wants to read anyone else's formulas. --
  Finman's Law of...
• Avoid overuse of 'quotation
  "marks...
• Don't overuse exclamation
  marks!!...
• Manually operated analog scribing device
  (description of...