diff --git a/kern/common-params.go b/kern/common-params.go
index d428678..56903b1 100644
--- a/kern/common-params.go
+++ b/kern/common-params.go
@@ -26,7 +26,7 @@ const (
 	ParamIterator  = "iterator"
 )
 
-// to be moved in its own source file
+// to be moved into its own source file
 const (
 	ConstLastIndex = 0xFFFF_FFFF
 )
diff --git a/operator-in.go b/operator-in.go
index 7700ad5..25e0ca0 100644
--- a/operator-in.go
+++ b/operator-in.go
@@ -10,6 +10,7 @@ import (
 	"git.portale-stac.it/go-pkg/expr/sym"
 	"git.portale-stac.it/go-pkg/expr/types/array"
 	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
 	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
@@ -46,6 +47,9 @@ func evalIn(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	} else if list.IsLinkedList(rightValue) {
 		ls, _ := rightValue.(*list.LinkedList)
 		v = ls.HasValue(leftValue)
+	} else if interval.IsInterval(rightValue) {
+		r, _ := rightValue.(*interval.IntervalType)
+		v = r.Contains(leftValue)
 	} else {
 		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
diff --git a/t_index_test.go b/t_index_test.go
index c8b2ffb..92a9ed3 100644
--- a/t_index_test.go
+++ b/t_index_test.go
@@ -45,10 +45,11 @@ func TestCollections(t *testing.T) {
 		/*  29 */ {`"abcdef"['x'..]`, nil, `[1:14] interval expression expected integer, got string (x)`},
 		/*  30 */ {`"abcdef"[1+..]`, nil, `[1:12] infix operator "+" requires two non-nil operands, got 1`},
 		/*  31 */ {`"abcdef"[1..4+]`, nil, `[1:15] infix operator "+" requires two non-nil operands, got 1`},
+		/*  32 */ {`r=-1..0..2; "abcdef"[r]`, "fdb", nil},
 	}
 
 	t.Setenv("EXPR_PATH", ".")
 
-	// RunTestSuiteSpec(t, section, inputs, 30)
+	// RunTestSuiteSpec(t, section, inputs, 32)
 	RunTestSuite(t, section, inputs)
 }
diff --git a/types/interval/interval.go b/types/interval/interval.go
index 487b4bd..475d2f7 100644
--- a/types/interval/interval.go
+++ b/types/interval/interval.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
 )
 
 const TypeName = "interval"
@@ -60,6 +61,17 @@ func (p *IntervalType) ToIntTriple() (b, e, s int) {
 	return
 }
 
+func (p *IntervalType) Contains(value any) (ok bool) {
+	if v, err := types.ToGoInt64(value, TypeName); err == nil {
+		if p.begin <= p.end {
+			ok = (v >= p.begin && v < p.end && (v-p.begin)%p.step == 0)
+		} else {
+			ok = (v <= p.begin && v > p.end && (v-p.begin)%p.step == 0)
+		}
+	}
+	return
+}
+
 // func (b *bool) EqualTo(other kern.Equaler) (equal bool) {
 // 	if otherBool, ok := other.(*bool); ok {
 // 		equal = b == otherBool