1. **State the problem:** Simplify the expression $$0.5 - [7 - 2 - (1 - 9) - 3 + 12] + 4.$$\n\n2. **Recall the order of operations:** Parentheses first, then brackets, then addition and subtraction from left to right.\n\n3. **Simplify inside the innermost parentheses:** $$1 - 9 = -8.$$\n\n4. **Substitute back:** $$0.5 - [7 - 2 - (-8) - 3 + 12] + 4.$$\n\n5. **Simplify inside the brackets step-by-step:**\n\nCalculate $$7 - 2 = 5,$$\nthen $$5 - (-8) = 5 + 8 = 13,$$\nthen $$13 - 3 = 10,$$\nthen $$10 + 12 = 22.$$\n\n6. **Substitute back:** $$0.5 - [22] + 4 = 0.5 - 22 + 4.$$\n\n7. **Perform the remaining operations from left to right:**\n\n$$0.5 - 22 = -21.5,$$\nthen $$-21.5 + 4 = -17.5.$$\n\n**Final answer:** $$-17.5.$$