For 5: The integral from its limit follows from the capital's usage as a summation  device as in series; the lowercase commonly denotes standard deviation in statistics.
For 10: The lowercase is used interchangeably with mu for density functions and  the limit of the capital may be represented as the integral.  For 5: The integral from its limit follows from the capital's usage as a summation  device as in series; the lowercase commonly denotes standard deviation in statistics.
For 10: The lowercase is used interchangeably with mu for density functions and  the limit of the capital may be represented as the integral.  
Sigma