This is the symbol of multiple integrals in advanced mathematics. Below the integral symbol is a definite integral interval, which is defined as a lifetime. The following d is a differential symbol, which is the object to be integrated. His two d's are T-time and idea. This place is where the original integral function is. He wrote it as do, which means to do, carry out and take action. If you have to explain the meaning of this formula, it is translated into vernacular: act for every minute and every idea for a lifetime.