Function differentiate 

pub fn differentiate(
    expr: &TLExpr,
    var: &str,
    config: &DiffConfig,
) -> Result<DiffResult, DiffError>

Symbolically differentiate expr with respect to the variable named var.

Differentiation rules

• d(c)/dx = 0 for any constant c
• d(x)/dx = 1
• d(y)/dx = 0 for y ≠ x
• Sum rule: d(a + b)/dx = d(a)/dx + d(b)/dx
• Product rule: d(a * b)/dx = a * d(b)/dx + b * d(a)/dx
• Quotient rule: d(a / b)/dx = (d(a)/dx * b − a * d(b)/dx) / b²
• Power rule: d(a^n)/dx = n * a^(n−1) * d(a)/dx (when exponent is a constant)
• Chain rule applies to transcendental unary functions
• Logical AND: d(AND(a,b))/dx = AND(d(a)/dx, b) OR AND(a, d(b)/dx)
• Logical OR: d(OR(a,b))/dx = OR(d(a)/dx, d(b)/dx)
• Logical NOT: d(NOT(a))/dx = NOT(d(a)/dx)
• Implication: expanded as NOT(a) OR b before differentiating
• Quantifiers: bound variable shadowed; derivative of body is returned
• Let-binding: full chain-rule expansion via d(body)/d(bound) * d(value)/dx

Errors

Returns DiffError::MaxDepthExceeded if the expression tree exceeds config.max_expr_depth. Returns DiffError::ExprTooComplex if an unsupported node is encountered and config.error_on_unsupported is true.