Let's create mathematical expressions using the numbers 5, 8, 12, and 6 exactly once in each expression. The goal is to obtain the numbers 1 through 13 as the results of these expressions.

1. $12 - 8 - 5 + 2 = 1$
2. $6 \div (12 - 8) + 5 - 6 = 2$
3. $12 - 8 + 6 \div 6 = 3$
4. $5 - 8 + 12 \div 6 = 4$
5. $12 - 8 + 6 - 5 = 5$
6. $(12 - 8) \times 6 \div 12 = 6$
7. $8 - 12 + 5 \times 2 = 7$
8. $8 + 5 - 12 + 7 = 8$
9. $8 + 5 - (12 \div 6) = 9$
10. $12 - 5 - 8 + 10 = 10$
11. $12 - 5 + 4 = 11$
12. $(12 \times 6) \div 12 + 5 = 12$
13. $(12 - 8) + (5 \times 2) = 13$

Would you like more details or explanations on how these expressions were formed? Here are 5 related questions for further practice:

1. Can you create a different set of expressions that evaluates to the numbers 1 through 13 using the same four numbers?
2. How would these expressions change if we added a fifth number to use in each expression?
3. Can you find another set of four numbers that can produce all the values from 1 to 13?
4. What happens if you restrict the operations allowed to only addition and subtraction?
5. Could you form the numbers 14 through 20 with the same set of numbers?

Tip: Breaking down each target number into possible operations can simplify the process of creating these expressions.