1638-3947:539-748[1839:1993]:18393=

To solve the expression \( 1638 - 3947 : 539 - 748 [ 1839 : 1993 ] : 18393 \), let's break it down into manageable parts.

However, please clarify your notation:

1. What does the colon ":" signify in your context?
2. What does the square brackets "[]" signify?

Are you asking to perform arithmetic operations, or is this a structure of some sort (like an equation)? Please provide more details so I can assist you better.