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OR function - Microsoft Support
Using IF with AND, OR, and NOT functions in Excel
Use AND and OR to test a combination of conditions
Video: IF with AND and OR - Microsoft Support
Logical functions (reference) - Microsoft Support
Create conditional formulas - Microsoft Support
IF function – nested formulas and avoiding pitfalls
Use nested functions in a formula - Microsoft Support
IF function - Microsoft Support
IFS function - Microsoft Support
Excel functions (by category) - Microsoft Support